It’s low tide in April off Captree Island, and the rumble of cars over the nearby Robert Moses Causeway is muffled by steady gusts whipping the top of Great South Bay. I wade with Chuck Westfall and Sean O’Brien of Thatch Island Oysters in water that barely reaches our knees, shallow enough to see through to the bottom: tufts of eel grass, coral-colored jellyfish and the ghostly outlines of rectangular mesh bags in neat rows.

These bags hold millions of oysters — five million, in fact — in a jumble of sizes and ages, from toddlers to teenagers to the almost-grown. The long, brutal winter means the water is chillier than it should be this time of year, about 58 degrees Fahrenheit, which is too cold for these oysters to have started growing again after their winter slumber. Donning sunglasses and waders, Westfall and O’Brien look like oyster secret agents as they haul bags from the water into the 19-foot Carolina Skiff that bobs beside them.

As the bags flop onto the deck, they soak my reporter’s notebook, lying nearby. Did I really need those notes, I think? Maybe, but I’d left my pad on the deck because it was nearly impossible to wade in bay water and write at the same time, and because I am occasionally hauling bags, too, and because touring an oyster farm so near to my hometown (Islip), after decades of gobbling them almost mindlessly, has my total attention.

Growing up near Great South Bay in the ’70s and ’80s, I had the impression that the bay’s greatest days were behind it — that the clams my grandparents consumed by the bucket were mostly gone, and the oysters that their grandparents ate before them, Blue Points, even longer gone. That most Blue Points now came from the Long Island Sound, off the coast of Connecticut.

The bay is not one to go quietly, though, and neither are its oysters. “They are as close to the original Blue Points » as you can get,” said Westfall, 66, a ruddy figure who grew up in Amityville and traded in a long career in sound engineering for a “retirement” spent farming oysters. Because we are about 20 miles west of Blue Point, Westfall calls these Fire Island Blues — a nod to their lineage, but also the swirling place where they are grown, these shallows close to the Fire Island Inlet.

Not all of his crop will make it to adulthood, for despite their calcified shells, oysters are sensitive creatures. Nearly two years of filtering phytoplankton (microscopic marine algae) out of bay water are interspersed with tough winters, the aggression of predators such as oyster borers and the so-called brown tides that can occur in the summer. Those thick algae blooms, caused by excess nitrogen from the runoff of an island where millions of people live, block sunlight and stunt oyster growth.

Raising oysters may be a business for Westfall, who began with 10,000 oysters seven years ago, but he’s also deeply concerned with the threats to their long-term future. Like miniature Brita filters, oysters belong in this bay — not only as food, but to cleanse and balance it. “Oysters are a keystone species here,” Westfall said. As president of the Long Island Oyster Growers Association, he’s a passionate advocate of redeveloping natural oyster reefs in the bay, which has long been more associated with its clam trade. “Oysters are much more efficient filter feeders [than clams], and are more resilient once they are given a proper place to live.”

We haul bags of full-grown oysters onto wooden-and-wire racks in the middle of the cove for an hour or more of sun bleaching, which will dry their shells and spiff them up for the trip from bay to boat to truck to restaurant. Some might even end up on an airplane at MacArthur Airport, bound for restaurants thousands of miles away, because the appetite for briny Eastern oysters (Crassotrea virginica) is seemingly boundless.

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After the racks are loaded, O’Brien, the younger of the two by about 30 years, guns the skiff’s outboard engine and points the boat toward a nearby dock topped by a gray outbuilding, a few tables and an oyster tumbler — basically, a horizontal cylinder made of heavy-gauge aluminum and shot through with holes. Westfall and O’Brien dump hundreds of almost-grown oysters onto a battered wooden table, their moonscape shells clacking as they fall. They’ll be shaken in the tumbler to strengthen their shells and deepen their cups, but before they’re returned to the water to continue growing, first things first. With a turn and flick of the knife, O’Brien opens one, severs the adductor muscle and hands it over — a glistening slick of protein, minerals and brine.

Nomenclature is tricky when it comes to Blue Point oysters. A 1908 New York law says Blue Points need to come from Great South Bay. Since New York law ends at the New York border, however, and since many diners equate Blue Points with a desirable baseline oyster, the name carries value, and so has been adopted by growers from Texas to Maine. Hence, $1 happy-hour oysters that are often called ‘Blue Points’ can vary wildly. The majority, though, come from Long Island Sound, just off the coast of Connecticut, where they are farmed en masse.

Blue Points migrated there through a series of misfortunes and marketing moves. The origin story of the real Blue Point — a meaty, tough-shelled oyster that thrived in Great South Bay in the 1800s, very near to the town whose name they carry — varies, depending on source. Supposedly discovered growing wild in the waters just south of Blue Point in the early 19th century, it’s possible their true roots lie farther south. In his 2007 book “The Big Oyster: History on the Half Shell,” author Mark Kurlansky relays the legend that Blue Point resident Joseph Avery seeded the bay with Chesapeake Bay stock when he returned home from the War of 1812. Whichever story is correct, soon all oysters from the bay were being called Blue Points, and New York City had such ardor for the bivalves that the original beds were soon decimated.

In turn, oyster hatcheries and farms sprung up by the mid to late 1800s to keep the by-then thriving Blue Point industry going. In the 1930s, two storms — one in 1931 that opened the Moriches Inlet, followed by the Hurricane of 1938 — delivered the last sucker punch to the bay’s oyster beds, and seemed to put the kibosh on Blue Points for good. Great South Bay became better known for clams — once supplying half of the country’s demand — but overharvesting and unceasing development on Long Island (and the accompanying runoff), depleted those stocks, too. Brown tides began arriving in the 1980s, and the clam harvest fell precipitously in the 1980s and 1990s.

What didn’t dissipate, though, was the hunger for shellfish — especially among a new generation of chefs. “During the sushi boom of the [late] 1980s, people began consuming oysters, and they became very popular again, and there was a big [oyster] boom in the ’90s,” Chris Quartuccio said. The Sayville native, who began harvesting clams from Great South Bay » at age 12, began to dive for wild oysters in Long Island Sound around 1995 and directly supply those to New York City chefs who wanted local shellfish.

Eventually, Quartuccio turned his attention back to Great South Bay and began seeding oysters there. “Everyone told me, ‘You can’t grow oysters in the Great South Bay, it’s not possible, they haven’t grown here in 70 years,’ ” Quartuccio said. But the site he leased, close to Fire Island Inlet, was kind to oyster production. “The tremendous exchange of water [there] enables the oysters to grow nice and fat and plump.”

Twenty-two years later, Quartuccio runs Blue Island Oyster Co., which harvests and sells an average of 200,000 oysters a week, including Fire Island Blues; Westfall became a partner in Blue Island a few years ago. “At any given time, there are oysters in the air or on a truck going to a restaurant somewhere else,” Quartuccio said.

Despite Long Island’s centuries-old oystering tradition, its South Shore is largely devoid of reefs or ideal conditions for the bivalves to naturally reproduce. That’s why Quartuccio, Westfall and other bay farmers need to “set” oyster seed along the bottom of the bay, typically relying on a few different hatcheries for their broodstock. If one has a problem, the thinking goes, the others can take up the slack.

About a third of Westfall’s Fire Island Blues are born along the shores of Peconic Bay in Southold at a place called Shellfisher Preserve. Here, marine biologist Karen Rivara breeds oysters from microscopic infancy to toddlerhood. She supplies at least 20 Long Island oyster farmers, but has to turn away many others. “The market is almost insatiable,” said Rivara as she checked tubes in a humid greenhouse. She is surrounded by towering, bubbling Pyrex tubes filled with neon-green algae that trickles into a subterranean bunker below.

In that underground warren of dim, cool rooms, oysters begin their lives when their parents, lined up in plastic trays filled with 68-degree water — the temperature of oyster love — expel their sperm and eggs to find each other. Soon, when the larvae are microscopic scuttering bumper cars, they are transferred by the thousands into plastic tanks, where they attach themselves to bits of shell to grow, becoming what is called spat. They then spend about four weeks in tanks, voraciously filtering algae in the upwelling and downwelling of constantly moving seawater, thus ensuring an uninterrupted supply of food. When the infant oysters are about the size of a grain of millet, they’re ready for growers such as Westfall to pick up.

Rivara, a kinetic 50-something with high cheekbones and sea-green eyes, was drawn into marine science after watching Jacques Cousteau as a tween. She seemed to foretell the oyster boom decades before it began in earnest, founding an oyster cultivation company in 1993.

“It’s hard to produce them, so that’s what I focus on,” Rivara said. “Every year, the water is different, the growing conditions are so different. When you’re successful at it, it feels really good, because at the end of the day, you have this animal you can hold in your hand that you helped produce.”

About 14 years ago, Rivara moved her shellfish farming here to Shell-fisher Preserve, the former home of the Shelter Island Oyster Co. — once owned by the Plock family and major driver of Long Island oyster farming until it closed in the 1950s. Now, the land is protected by the Peconic Land Trust. If you find yourself eating, say, a Peconic Gold or Montauk Pearl, there is a strong probability that the bivalve began its life here.

At Shellfisher, Rivara keeps some of her own seed to raise to maturity, and she calls them Peconic Pearls. They’re petite and almost savory, and five cents from each retail sale goes to efforts to preserve the Peconic Estuary. (Rivara also raises oysters across the Sound, near Mystic, Conn.) As with many Long Island waters, said Rivara, the Peconic Bay remains threatened by excess nitrogen and hence, brown tides and imbalances that imperil oysters. “What we put into the ground ends up in the bay,” Rivara said. Those algae blooms stunt oyster growth — though she is quick to emphasize they don’t affect flavor. “It’s not that nitrogen is a poison. There’s just an excess amount of it.” »

When it comes to finding Long Island oysters that have absorbed the tide-beaten “merroir” of Great South Bay — including Maris Stellas, Sexton Island True Blues or Lucky 13s — it can be harder here than in New York City.

The cozy Catch Oyster Bar in Patchogue, which opened in 2017, is one of only a handful of places on the Island that recognizes and celebrates the subtle differences in the area’s oysters. Here, co-owner (and chef and shucker) Michael Avino changes his oyster board daily to reflect the microlots of local oysters that arrive here throughout the week — including Fire Island Blues — along with their places of origin, size and salinity levels.

Avino created Catch with his father, James, to capitalize on a few trends: That of buzzy Patchogue, as well as the ever-growing demand for oysters and clams. But he also donates his spent oysters shells to the Friends of Bellport Bay to begin new underwater oyster reefs. “Oysters are hip now, and oyster farms are cropping up all over Long Island,” said Avino, a former live-events coordinator at MTV. Growing up, Avino’s father was a former clammer, and his friends were baymen. Those relationships persist. “I’m getting oysters that were in the water that morning, and freshness counts for so much.”

Avino likens eating a fresh oyster to being hit by a wave when out in the ocean and having the water splash into your nose and mouth. “It’s that salty ocean essence that you’re left with,” Avino said. The chubby Fire Island Blue is the house oyster at Catch, presented not only on the half-shell with a red-wine mignonette, but also roasted and served piping hot, topped with butter, garlic and Parmigiano Reggiano.

As a lifelong oyster lover, I’ve eaten them every which way. Few are as memorable, though, as the one I hold in my hand in the middle of Great South Bay, where the tide is coming in and O’Brien is busy shucking. Its shell is thick, its meat plump and filling the shell, a gloss of liquor around the edges. I tip it into my mouth, and the slippery knot of brine and the resonant tingle of minerals slips down my throat.

O’Brien eats one, too, and we chuck the shells into the water.

WHERE AND WHEN TO EAT OYSTERS ON LONG ISLAND

Oysters were historically harvested only from September to April, outside their summer spawning season. (After oysters spawn, they turn flaccid and watery.) Though triploids, or non-spawning asexual oysters, are becoming more common, it’s fair to say that oysters are at their best from fall (when they’ve built up their winter stores of glycogen, a sweet carbohydrate compound) to early spring. For a variety of small-production Long Island oysters, here’s a handful of places to try: